The present invention relates to a process for preparing alkynediols by reacting acetylene with carbonyl compounds in the presence of basic catalysts.
Alkynediols are valuable intermediates for preparing, for example, low-foam surfactants, pyrethroids, electrolysis auxiliaries or peroxides.
Various methods of preparing alkynols are known. They can be roughly divided into reactions catalyzed by transition metals and base-catalyzed reactions.
W. Reppe, Liebigs Anm. Chem. 1955, 596, pages 1 to 3, describes, for example, the carbonylation of acetylene with carbonyl compounds in the presence of acetylides of heavy metals of the first transition group of the Periodic Table of the Elements in THF.
On pages 6 to 11 and 25 to 38 it is stated that the ethynylation of ketones can be carried out in aqueous media using alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates or tertiary amines as catalysts. In addition, copper acetylide can be used as catalyst. In the examples, the preparation of methylbutynol from acetone and acetylene in water using potassium hydroxide as catalyst is mentioned.
R. J. Tedeschi et al., J. Org. Chem. 1963, 28, pages 1715 to 1743, describe the base-catalyzed reaction of acetylene and phenylacetylenes with carbonyl compounds in liquid ammonia under superatmospheric pressure. Here, the reaction to give the corresponding secondary and tertiary acetylenic carbinols is carried out using catalytic amounts of sodium hydroxide or potassium hydroxide.
B. A. Trofimov, Russian Journal of Organic Chemistry, Vol. 31, No 9, 1995, pages 1233 to 1252, describes various reactions using acetylene. Mention is made, inter alia, of ethynylations using the superbasic system KOH/DMSO.
J. H. Babler et al., J. Org. Chem. 1996, 61, pages 416 to 417, describe the alkoxide-catalyzed addition of terminal alkynes onto ketones. Here, the reaction is carried out using tert-butoxide as catalyst. The preparation of alkynediols is not mentioned.
Alkynediols have hitherto been prepared only with use of at least stoichiometric amounts of base. For this purpose, use is frequently made of nucleophilic potassium bases in aprotic solvents, cf. J. Org. Chem. 1963, 28, pages 2480 to 2483 and J. Appl. Chem. 1953, pages 39 to 42, and also EP-A-0 285 755.
It is an object of the present invention to provide a process for preparing alkynediols which avoids the disadvantages of the existing processes and requires the presence of only catalytic amounts of bases.
We have found that this object is achieved by a process for preparing alkynediols of the formula (I)
R1R2C(OH)xe2x80x94Cxe2x89xa1Cxe2x80x94C(OH)R1R2xe2x80x83xe2x80x83(I)
where
R1, R2 are each independently H, or a C1-20-hydrocarbon radical which may be substituted by one or more C1-6-alkyls and/or be interrupted by nonadjacent heteroatoms and/or contain Cxe2x80x94C double or triple bonds,
by reacting compounds of the formula (II)
R1xe2x80x94C(xe2x95x90O)xe2x80x94R2xe2x80x83xe2x80x83(II)
with acetylene in a polar aprotic solvent in the presence of basic alkali metal salts, preferably alkali metal alkoxides, as basic catalysts.
It has been found that alkynediols can be obtained in high yield when using alkali metal alkoxides in polar aprotic solvents.
The alkali metal alkoxides can be lithium, sodium, potassium, rubidium or cesium alkoxides. Preference is given to using potassium alkoxides as basic catalysts.
The alcohols on which the alkali metal alkoxides are based are particularly preferably selected from among alkynols of the formula (III)
xe2x80x83R1R2C(OH)xe2x80x94Cxe2x89xa1CHxe2x80x83xe2x80x83(III)
where R1 and R2 are as defined above, and straight-chain or branched C1-12-alkanols.
The basic catalyst can also be prepared in situ from alkali metal hydrides, acetylene and the compound of the formula (II).
In the reaction, certain amounts of alkynols of the formula (III) are also formed in addition to alkynediols. For this reason, the use of these compounds or preparation of them in situ is advantageous. Otherwise, particular preference is given to using a potassium C1-6-alkanolate, for example one selected from among potassium methoxide, potassium ethoxide, potassium propoxides, potassium butoxides, potassium pentoxides or potassium hexoxides. The alkanolates can be straight-chain or branched.
The basic catalyst is preferably used in an amount of from 5 to 65 mol %, particularly preferably from 10 to 30 mol %, based on acetylene.
The reaction is preferably carried out at from xe2x88x9220 to +60xc2x0 C., particularly preferably from xe2x88x9210 to +40xc2x0 C., in particular from 10 to 30xc2x0 C., and at a pressure of from 0.1 to 10 bar, particularly preferably from 0.5 to 5 bar, in particular atmospheric pressure.
The polar aprotic solvent is preferably selected from among tetrahydrofuran (THF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO) and mixtures thereof, with up to 20% by weight of the solvent being able to be replaced by nonpolar hydrocarbons. The solvent is particularly preferably based on THF. In particular, the proportion of nonpolar hydrocarbons is less than 10% by weight, especially less than 5% by weight. In particular, only THF is used as solvent.
In the reaction of the present invention, it is possible to use a wide variety of carbonyl compounds of the formula (II). Preferably R1and R2 are each independently H or a C1-2-hydrocarbon radical which may be straight-chain or branched. Particularly preferably, R1 and R2 are independently H or C1-6-alkyl. Examples of suitable carbonyl compounds are formaldehyde and acetone.
In the process of the present invention, the basic catalyst is preferably initially charged in the polar aprotic solvent, whereupon acetylene and the carbonyl compounds are metered in and reacted in parallel. The mixture can then be worked up hydrolytically.
The invention is illustrated by the examples below.